The present invention relates, in general, to a machining apparatus for making a plasticizing barrel, and more particularly to a machining apparatus for providing a plasticizing barrel with at least one conical bore for accepting a plasticizing screw.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Conical twin screw extruders typically have converging screw axes as well as a converging screw configuration. As a result of the decrease in the outer diameter, the volume of the C-shaped transport compartments is continuously reduced as the distance to the intake zone increases. This causes a continuous compaction. The conical twin screw can be constructed with sections of different but constant helix angle. As the consequence of the conicity, the screw tip has a reduced diameter so that a smaller screw back pressure is experienced at constant melt pressure as in cylindrical screws.
To date, the manufacture of plasticizing barrels with conical screw bores for such conical twin screw extruders has proven difficult because, on one hand, the screw bores converge conically toward one another in conformity with the configuration of the conical screws, while on the other hand, the bore axes extend to one another.
Plasticizing barrels for conical twin screw extruders are typically manufactured heretofore by firmly clamping the plasticizing barrels and then machining a first cylindrical screw bore by means of a deep drill. Then, a coarse conical configuration is realized by using cutting tools that replicate the conical profile of the screws. Finally, conical grinding tools are used for carrying out fine-machining steps. This manufacturing process takes very long and is not only complex but also cost-intensive while still not resulting in a desired quality of the inside surface of the screw bore.
It would therefore be desirable and advantageous to provide an improved machining apparatus which obviates prior art shortcomings and which allows a manufacture of high-quality plasticizing barrels with conical screw bore.